1. Field of the Invention
Aspects of the present invention relate to a secondary battery, and more particularly, to a secondary battery capable of preventing an electrode assembly from being deformed when a longitudinal compression of the secondary battery is evaluated and of preventing a short between electrode plates in accordance with the deformation of the electrode assembly.
2. Description of the Related Art
Recently, as portable electronic apparatuses are rapidly becoming smaller and lighter, research on secondary batteries used as a driving power source has increased. A nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, and a lithium secondary battery are examples of secondary batteries.
Among the above batteries, the lithium secondary battery may be rechargeable and may be made small yet with a large capacity. Since the lithium secondary battery has a high driving voltage and a high energy density per specific weight, the lithium secondary battery is widely used in a high-technology electronic apparatus field. The lithium secondary battery is formed by accommodating an electrode assembly consisting of a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate in a can together with an electrolyte, and by sealing the upper end of the can with a cap assembly.
The electrode assembly is formed by winding the positive electrode plate, the negative electrode plate, and the separator interposed between the positive electrode plate and the negative electrode plate. A positive electrode tab is coupled to the positive electrode plate to protrude toward the upper end of the electrode assembly. A negative electrode tab is coupled to the negative electrode plate to protrude toward the upper end of the electrode assembly. In the electrode assembly, the positive electrode tab and the negative electrode tab are separated from each other by a predetermined distance and are electrically insulated from each other.
The cap assembly includes a cap plate, an insulating plate, a terminal plate, and an electrode terminal. The cap assembly is coupled to an additional insulating case to be coupled to the upper end opening of the can and to seal the can.
A groove for the positive electrode tab and a hole for the negative electrode tab are formed in the insulating case. The insulating case is inserted in order to prevent a short between the top of the electrode assembly and the bottom of the cap assembly that are accommodated in the can. In addition, the insulating case prevents a short that may be generated by the curved negative electrode tab and positive electrode tab contacting the internal wall of the can.
The lithium secondary battery having the above structure becomes thin while the energy density increases so that the lithium secondary battery is vulnerable to shock and compression. When shock or compression is applied to the lithium secondary battery, the electrode assembly accommodated in the can is deformed and the lithium secondary battery is ignited or exploded due to a short between the electrode plates caused by the deformation of the electrode assembly.
In particular, when the lithium secondary battery is deformed by longitudinal compression force (perpendicular to the longitudinal axis) in the longitudinal compression test that is one of the safety tests of the lithium secondary battery, the step difference formed in the top of the can to a height by the thickness of the cap assembly in order to settle the cap assembly is curved toward the inside of the can and is deformed. Therefore, the step difference deforms the electrode assembly while applying local pressure to the top of the electrode assembly accommodated in the can so that the short is generated between the electrode plates.